IndexOf () when array elements are objects (javascript)
6 answers
You need to loop at one point. But you can abstract it to look like you are not looping
function indexOfCallback(arr, callback, startIndex) {
if (typeof startIndex == 'undefined') {
startIndex = 0;
}
for(var i=startIndex; i < arr.length; i ++) {
if (callback(arr[i])) {
return i;
}
}
return -1;
}
var array = [{id:1, value:5},{id:2, value:6},{id:3, value:7},{id:4, value:8}];
// Search on id === 3
console.log(indexOfCallback(array, function(obj){
return obj.id === 3;
}));
// Search on value === 6
console.log(indexOfCallback(array, function(obj){
return obj.value === 6;
}));
As Anthony mentioned, this is proposed for ECMAScript 6. Here's a more complete polyfill https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex
if (!Array.prototype.findIndex) {
Array.prototype.findIndex = function(predicate) {
if (this == null) {
throw new TypeError('Array.prototype.find called on null or undefined');
}
if (typeof predicate !== 'function') {
throw new TypeError('predicate must be a function');
}
var list = Object(this);
var length = list.length >>> 0;
var thisArg = arguments[1];
var value;
for (var i = 0; i < length; i++) {
value = list[i];
if (predicate.call(thisArg, value, i, list)) {
return i;
}
}
return -1;
};
}
console.log(array.findIndex(function(obj){
return obj.id === 3;
}));
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arrayElements.map(o => o.id).indexOf(3);
Notes:
- Possibly slower than loop because it transforms the entire array before searching. But with high level languages like Javascript, you never know.
- Infinitely more readable than a loop.
- IE compatible (as opposed to findIndex from 2017).
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I wrote a function for you that you can use to get the job done, but uses a loop:
var yourObjArray = [{id:1, value:5},{id:2, value:6},{id:3, value:7},{id:4, value:8}];
function objArrayIndex(objArray){
for(var i = 0; i < objArray.length; i++){
if(objArray[i]['id'] == 3){
return i;
}
}
return -1;
}
console.log(objArrayIndex(yourObjArray));
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In such an array, you cannot get access items by id. Therefore, using a loop is the best solution you have. However, depending on your use case, you might also consider using an object instead of an array for direct access.
var container = { 1: {id:1, value:5}, 2: {id:2, value:6}, 3: {id:3, value:7} }
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You can use Array.forEach I think
var fooArray = [{id:1, value:5},{id:2, value:6},{id:3, value:7},{id:4, value:8}];
var foundIndex = -1;
fooArray.forEach(function(el, index){
if(el.id==3) {
foundIndex=index;
return false;
};
});
//foundIndex = 2
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You can use an array filter, but I think you will get a better solution using a loop.
var array = [{id:1, value:5},{id:2, value:6},{id:3, value:7},{id:4, value:8}];
var result = array.filter(condition);
function condition(value, index){
if (value.id === 3) return index;
}
console.log(result);
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